The Kerch Strait incident has the makings of a geopolitical emergency.
The clash at sea Sunday between Ukrainian and Russian vessels already prompted an emergency UN Security Council meeting and, in Ukraine, a push for martial law.
Now, all eyes will be on how the White House -- and its unpredictable occupant -- will react this week.
President Donald Trump is set to attend the G20 Leaders Summit this week in Buenos Aires, where he is expected to have a one-on-one meeting with Russian President Vladimir Putin. Officials in Moscow have set expectations of wide-ranging talks between the two leaders, with arms control at the top of the list.
But this new crisis, with Russian boats opening fire on and seizing three Ukraine naval ships near Crimea, changes the equation for the meeting.
For starters, there are questions about how Trump will respond to Russia's bid to exert control over waters it shares with Ukraine. A 2003 agreement confirms the Azov Sea and the Kerch Strait as domestic waters of Russia and Ukraine. But during Sunday's confrontation, the Russians closed traffic through the strait, blocking an important economic lifeline for Ukraine. It later reopened the strait for civilian ships.
Moscow's move raised alarms in Europe. In a tweet, German Foreign Minister Heiko Maas said the developments around the Kerch Strait were a "worrying" development.
"A Russian blockade of the thoroughfare into the Azov Sea is not acceptable," he said. "It is important to lift this blockade. We call on both sides to de-escalate."
Trump, by contrast, did not immediately comment, and his silence on Twitter spurred some critics to wonder whether his administration would take a tough line with Putin.
On the day of the incident, Anders Åslund, resident senior fellow at the Atlantic Council, a prominent think tank, wrote on Twitter: "Today @realDonaldTrump has written 9 tweets but none about the biggest question today: Russia's new military aggression in Ukraine, seizing 3 naval ships & blocking the international waters of the Azov Sea. Retweet if you think Trump must not see Putin at the G20 in Argentina!"
Steven Pifer, a former US ambassador to Ukraine, also noted the silence from the White House and Washington.
"#EU statement on #Russia's escalation of crisis with #Ukraine in Kerch Strait could have been stronger, but at least they said something," he wrote on Twitter Sunday. "Any word from White House or Washington?"
The Trump-Putin meeting in Buenos Aires looks set to go full steam ahead. Asked Monday by CNN whether the crisis had an impact on plans, Kremlin spokesman Dmitry Peskov said the meeting was still in the works.
"This meeting is being prepared, the Russian president is getting ready for the upcoming official visit to Argentina, which will take place on November 30, and to participate in the G20 summit, as well as for the bilateral meetings which are in his schedule on the sidelines of this summit, including a meeting with US President Trump," he said.
Trump's language about the Kerch Strait crisis and Crimea matters. The Kerch Strait has strategic and symbolic importance for Russia: It's the closest point of access for Russia to Crimea, the Black Sea peninsula Moscow annexed from Ukraine in 2014.
When Putin opened a bridge across the Kerch Strait in May, it sent a defiant message: The annexation of Crimea, unrecognized by most of the international community, was a closed matter.
In past statements, Trump has often blamed the annexation not on Putin, but on his own predecessor, President Barack Obama.
"Crimea was TAKEN by Russia during the Obama Administration," Trump wrote on Twitter in early 2017. "Was Obama too soft on Russia?"
But Trump now finds himself in a new position in the run-up to his meeting with Putin. He's the one who might have to find a way to talk tough with the Kremlin leader.